Polyphase transformer



Jan. 1l 1927.

E`. c. M. sTAl-n.l

POLYPHASE TRANSFORMER Filed dan. 20, 1922 30 cal manufacture.

enema Jan. 11, 1927.

UNITED STA res niermann c.

l 1,614,161 PATENT f OFFICE.-

n. STAHL, or' YoNxnas, NEW Yoan, AssIeNon To rrrrssnaen rraANsromanacommun neuronas-N or' rnNNsYLvANI'A.

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Application :11e- 1 January ao, 1922. serial No'. 5301.131.

This invention relates to 'polyphase transformers and particularly tothe arrangement of the various -parts of the magnetlc coreY Y withrespect to the paths furnished for the 51 magnetic flux linked with theelectric circuits.

The olyphase transformer-,is generally preferagle to the use of aplurality of single )hase transformers by reason `of economy 10 1n thecost of material and manufacture and lowered operating expense.I InsomeA forms of polyphase transformers, -part1c` ularly those o thelsimplest construction the` paths furnished for the ma etizing 15 flux ofthe different phases are neit er equal in magnetic reluctance norsymmetrical in their spa'ce relation. `For this reason there is a lo ofeicien an unbalanced icon ition -in the poly hase magneticrelationshipwhichvis reflecte intoI the exciting electric circuits and which .re-`

sults in' objectionable variations in the effecivevvalue of the excitingcurrentbetyveenthe various phases,- with attendant greater Varig'instantaneous values ,of excit- 1,

Nations` in the 'ingcurrents.. l

' 4One object ofmy invention is to roduce an eicientpolyphasetransformer o a simple"f0rm of construction capable of economi-Another object is to provide `magnetic paths for the flux from each ofthe coils rwhich will beso related as to give a substantially balancedrelation of the niagneticcircuits and have substantially the :15 samemagnetic reluctance, even though the core structure is unsymmetrical asto the space relationship between'all of the core legs carryingwindings. Another object is to produce a polyphase transformer which 40will not only have low core loss and high efficiency, but alsolow,balancedv and sym mctrical phase exciting currents both eHective andinstantaneous. advantages of my inventionwill be under stood byreference to the following descripn tion and accompanying drawingsilliistrating one embodiment thereof, this particular ein-- iwfliinentillustrating a :formof a three phase "former".

l is a face view of a vcere with the s diagrammatically indicated;lliig, an end vie and Fi 'il vertical i the line armee rc is' built upof an DE* in the core itself and y Other. objects and tial.

CC in the same planey carrying theusual vprimary kwindings indicated atP1, P2, P3

of a three-phase circuit and Vcorresponding secondary windings indicatedat Sp1, S2, S'J. Thev three core legs are joined at their upper andlower endsby the sections A, B, C and A', B', C respectively. .The up erends of legs A A and C IC are also indhpendently connected by thesection D of the core and their lower ends by section Di, leaving smallA.air spaces E, E' between the outer sections D, D and the inner sectionsof the core whichA join the three legs. Instead of having an air space,a layer of non-magnetic material may if desired be interposed betweenthey connecting sections ,but the magnetic separation. of the adjoiningconnecting sections should.besuiiicientlyv great to secure the re. sultsjdesired. vThe width of the face of strips D D" will be vsufficient tocause. `the magnetic yreluctance of the paths A D C -and A D Citoapproximately equal the reluctance of the paths A B and A B; or thestrips may be otherwiseso-porportioned or related to each other as tosubstantially ful fill this condition'. The core will be built upotlayers to the desired thickness, the layers being formed of sectionscut to suit the preference of the designer as to form and manner ofassembling.

Referring to Fig. l, the magnetic reluctance between the points A-A, B-Band C-C is substantially the same. The yoke portions AB, B C, A', B andB C` have substantially'the same magnetic reluctance. The pathsfurnished to theilux created by current in the coil P1 are A B B A and AD C C D A. ,'Due to the'fact that the legs and yolres `traversed by themagnetic flux in each part of 4the magnetic circuit are tentialv due tothe iniiuencs ci coil P1 alone and consequently there is tlienynomateriel interchange of i'iu: aetween them; iiltewisc the poi s *i atthe same poten- @i ent. of core Aparts there 1X, created hy the cur totwo parts when it L; A.' A and places the vrrespectivrely substantiallyequal to each other two other legs B B and C C in the same magneticrelationship with respect to the leg A A.

In the same way it may be shown that the tiux created by coil P2 has thetwo equal paths B C C B and B A A B to circulate in, and that there isno interchange of flux between A and C, and A and C through A D C and AD C', under the influence of coil P2. The same condition holds tor thetwo ilux pathsslinlred'with coil l", namely C B B C and C D A A D C. 1nthis case there is no material interchange et linx between A B and A Bdue to the influence of coil l.

It is understood that the eli'cct ot leakage flux has been neglected andonly the flux paths within the magnetic core itselt' have heendescribed.

rl`he net effect of the arrangement when having properly proportionedparts is to produce a polyphase'core in which the inagnetic relationshipbetween the portions carrying the windings is mutually symmetrical, andin which a balanced interchange ot' polyphase flux takes place in thesame general manner that it does in a poly- )hase core havine snice sYmmetr h yWith my improved construction separate paths for the fluxareprovided between each combination ot' any two legs, and all individualliux paths pass through at least two windings oi diitcrentphase's.

It will be evident that by use of my invention I produce apolyphaselcore for static inductive apparatus which gives a symmetricaland balanced magnetic relationship which reacts on the electric circuitsto produce balanced electric relationship, even though the core issoarranged that the electric coils are unsynnnetrically sprued; also lobtain a polyphase core olE strong and relatively simple mechanicalconstruction having correctly balanced polyphase mag netic interactionsresulting in high eiliciency.

Although I have described my invention with reference to a three phasetransformer. it is evident that it may be applied to polyphasetransformers of a diii'erent number of phases, and connections or" thecoils torming the electric circuits, may of course be such as to suitthe particular requirements without departing from the scope ot myinvention. It will also be understood that my invention may be embodiedin `modified forms of construction without departing' from the scopethereof.

I claim l. Apolyphase transformer having a core providing a plurality ofbalanced magnetic circuits of equal reluctance for the magnetic tiuX ofeach ot the polyphase circuits, said core being formed et inner andouter legs and core portions connecting said legs,

windings on each of said legs magnetically interlinked with all of theremaining windings, said core connecting portions providing differentaths for the magnetic iux passing throng 1 an inner leg from the pathsprovided for the tlux passing through and between the outer legs.

A transformer having a core formed of inner and o`uter legs and aconnecting portion joining said legs, said connecting portion' beingformed with a slot spaced from and extending across an end ot' an innerleg and dividing the connecting poi'- tion into an outer and inner part,the outer partbeing oli greater cross section than the inner part.`

3. A transformer havin(r a core formed of inner .and outer legs andconnecting portions joining said legs, said connecting portions beingformed with slots spaced from and extending across the ends ot an innerleg and dividing the connecting portions into outer and inner parts7 theouter parts being ot greater cross section than the inner parts. Y

4. A. transformer comprising a core having legs, the distances betweenone leg 'and each of two other legs being dierent and polyphase windingslocated on and bounded by substantially the same two parallel planes,said-core having portions connecting legs other and independent portionsconnecting legs which are fart n' distant from one another, all ot' saidportions providing flux paths ot substantially the same magneticreluctance.

5. A core tor a polyphase transformer having an inner leg adapted toreceivea winding, said core being formed with slots extending across andspaced from the ends ot said inner leg.

(l. A polyphase transformer comprising a core having legs, the distancesbetween one leg and each ot' the two other legs being different, andsaid core having' yoke portions joining said one leg with each oftheother legs, said yoke portions having substantially the sainemagnetic reluctance from said one lee' to each ot said other legsrespectively.

l. Stationary induction apparatus comprising a plurality of windings,means for supporting said windings -in spaced rela tion such that thedistance between one ot said windings and a second winding is dilerentfrom the distance between the said one winding and a third winding,means forming a magnetic circuit between said one winding and saidsecond windingA` and means forming a magnetic circuit ot the samemagnetic reluctance between the said one winding' and the said thirdwinding.

iEDlllvilltD C. it". S'lllil'lli.

separate legs.

which are near to one an-` lll() lill)

